This might not apply directly but to me it's like the saying that goes "If anything is worth doing, it is worth doing well"
There are 2 value judgments that need to be made here
1) Figuring out what is "worth doing" for you
2) Figuring out how to measure if you're "doing well"
For question 1, there's a high probability that the "worth doing" here is not just about what profit we make but rather whether we feel that we are making a difference with what we are doing. You mentioned in your OP that you are interested in healthcare which is not a minor investment of time as a career. Which part of healthcare would be the one that you think will give you the most satisfaction based on the effort you put in? What sort of global impact do you wish to achieve? Cure a disease such as cancer? Make healthcare more affordable?
As was suggested by SubtleFighter, start from your end-goal(s) and work backwards. If you have a rough outline of what you need to do to achieve your end-goal, then you can better judge if it will be "worth doing".
Question 2 is more of a challenge for Idealists like us who tend to aim for such high, lofty goals that we get demotivated when we fall short. Again, work backwards from your big goal and divide it into sub-goals in smaller time-frames that are achievable so that you can at least see yourself as successfully working towards your dream. It's great to have a dream of Solving the world's hunger problem, for example, but we need to have some practical milestones and ways to measure if we are actually going anywhere. Besides, most of the BIG problems can't be solved by a single person anyway so why put all the burden on just your shoulders? Figure out how and how much you can contribute to solving the whole puzzle.
I have "What I feel is convenient enough is the key" written on the whiteboard of my cubicle. It's not really about coming up with the perfect solution. It's about coming up with one that works well enough and most importantly, be practical in terms of things such as cost, implementation, etc.
Good luck in finding your spot in the Universe